This invention relates generally to forage harvesters, and particularly to improved knives therefor and a method of sharpening.
Forage harvesters typically collect crop material from the field, chop or reduce the material to substantially uniform lengths by means of a rotating cutterhead, and deliver the material to a trailing forage wagon or similar carrier. The vast majority of the harvesters being used today utilize a cylindrical or reel-type cutterhead which cooperates with a stationary shear bar parallel to the cutterhead axis to cut the material as it is fed over the shear bar into the cylindrical cutting path of the cutterhead.
The most common cutterheads comprise an axially mounted support structure having a plurality of individual knives fixed on the periphery thereof. The cutting edges of the knives may be arranged parallel to the axis of the cutterhead; however, it has been found very advantageous to provide knives that extend in a generally diagonal direction relative to the cutterhead axis and the shear bar, so that the knives shear the material rather than chop it. In this latter configuration, the edges of the knives can only trace a true cylindrical path if the knives are also twisted in addition to being bowed so that the knives form an approximately spiral-like segment of a cylinder.
The operational environment of forage harvesters is such that all component parts, and particularly the knives and cutting edges, are continuously subjected to tremendous potential damaging forces. Additionally, the nature and texture of the crop materials being operated upon are such that the cutting elements are abrasively acted upon to further impede consistantly efficient operation. Because of these working conditions, the cutterhead knives require relatively frequent sharpening by, in many cases, integral knife grinding equipment. Much effort has been expended by the industry to reduce the frequency of sharpening and the time required to accomplish it, and at the same time increase the useful life span of the cutting edges. For example, U.S. Pat. Nos. 3,805,660 and 3,635,271 teach the selective application of wear-resistance surfaces to the cutting edge and/or shear bar to promote "self-sharpening".
The increased efficiency sought by the industry has resulted in numerous different blade configurations, sharpening procedures, and blade mounting hardware. The wide range of blade designs can be seen by a view of the drawings in U.S. Pat. Nos. 3,452,796; 3,635,271; 3,677,316; 3,817,464 and 3,729,143. These same patents also show numerous approaches to knife mounting which manufacturers have developed to overcome the efficiency problems. Of particular interest is U.S. Patent No. 3,677,316 which discloses, in the specification and drawings thereof, some of the prior art techniques for sharpening cutter blades. U.S. Pat. No. 2,594,583 also shows a cutter knife design; however, the design is "underbeveled", i.e., the beveled edge is directed toward the center of the cutterhead, as opposed to the conventional opposite arrangement shown in, for example, U.S. Pat. No. 3,677,316.
The invention to be described below is a practical advance in the art which definitely decreases the amount of time necessary to sharpen cutterhead knives and additionally promotes increased efficiency of forage harvester operation.